The long term objectives of this research "revised" plan are to study the morphological and cytochemical details of developing synapses, the effects of defferenting lesions on these structures and to relate these findings to normal synaptic development and synaptic reorganization or plasticity. conventional light (LM) and electron microscopy (EM) will be specifically supplemented in this renewal application with LM and EM immunocytochemical localization of transmitters. The olfactory system will be used as the model. Immunoperoxidase techniques for selected neurotransmitter systems specified for the region will be used to demonstrate the pattern of development and the cytochemical alterations during synaptic degeneration and reorganization. Details of the immunocytochemical characteristics associated with developmental plasticity will be the major/specific aim of the renewal application. Deafferentating lesions will be placed at previously determined "critical ages" of synaptogenesis and the acute and chronic effects studied by LM and EM. Special attention will be given to deafferented sites and the immunoreactivity of the terminals involved in the plastic reorganization, possibly the reinnervation of these sites. LM will be used for quantification and EM for analyzing the membrane-related qualitative alterations. The principal questions to be answered are: What are the transmitter-related enzymes of the developing degenerating and reinnervating terminals? How does the pattern of immunolabelling change during development and following deafferentation and how are these related to the stage of synaptogenesis when deafferented? The results should provide heretofore unavailable information on changes in transmitters and receptors associated with developmental plasticity and synaptic reorganization.